In recent years, laser technology has been markedly developed. In particular, small-sized solid laser devices or semiconductor laser devices emitting a light in the near-infrared to infrared range with a high output have become easily available. These laser devices are extremely useful as a light source for exposure in direct plate-making based on digital data from a computer or the like.
Lithographic printing plate materials adapted for infrared laser contain an alkaline aqueous solution-soluble binder resin and an IR dye capable of absorbing a light to generate heat as necessary components. In non-exposed areas (image areas), the IR dye functions as a dissolution inhibitor which substantially decreases solubility of the binder resin due to mutual action with the binder resin and, in the exposed areas (non-image areas), the mutual action between the IR dye and the binder resin is so weakened due to generated heat that the exposed areas are dissolved away with an alkaline developing solution to form a lithographic printing plate.
In order to realize a highly useful one as the above-described lithographic printing plate, there are two technical subjects of 1) attaining a high uniformity of the image-forming layer and 2) attaining a high hydrophobicity in image areas and a high removability of non-image areas by development.
Uniformity of image areas technically relates to mainly the above-described production steps, and original printing plates (i.e., printing plate precursors) having an insufficient uniformity show a seriously deteriorated degree of fundamental performance required for printing plates that many sheets of printed products with a high image quality be stably provided, thus not being preferred. Also, a high hydrophobicity of the image areas is important from the viewpoint that, by enhancing endurance against a developing solution in the plate-making steps, there are obtained an excellent resolving power and a sufficient durability or a sufficient ink-depositing properties in the printing steps. However, too high hydrophobicity of the image areas might possibly cause reduction in solubility of the image areas in an alkaline aqueous solution commonly used as a developing solution, leading to unfavorable results such as development failure of non-image areas and generation of a sludge component in the developing solution.
That is, to say in a simplified manner, hydrophobicity of image areas and removability of non-image areas require the image-forming layer to have conflicting properties, and development of technology capable of attaining the both properties at the same time has been a difficult and important subject to be solved.
With respect to the technical subject, it has been known that it is useful to use a composition containing a high molecular compound having fluoro aliphatic groups as an image-forming composition.
Specifically, there have been disclosed the effect of more improving the function of realizing uniformity of the film resulting from improvement of surface-activating ability; the effect of solving the problem of development delay due to hydrophobicity; and the effect of forming a contrasty image by attaining both hydrophobicity of image areas and removability of non-image areas utilizing hydrophobicity-orientating power.
For example, Japanese Patent (Application) Laid-Open No. 187318/2000 discloses an image-forming material excellent in solubility discrimination between image areas and non-image areas using a high molecular compound containing monomer units having two or more fluoro aliphatic groups.
Also, Japanese Patent (Application) Laid-Open No. 288093/1999 discloses that an image-forming material showing an improved stability before being developed and an excellent handlability can be obtained by using a specific fluorine-containing polymer.
As is described hereinbefore, an image-forming layer containing a fluoro aliphatic compound is effective as a technique for attaining the aforesaid technical subjects 1) and 2) which are commonly shared by image-forming layers for the original lithographic printing plate (i.e., the lithographic printing plate precursor). However, the effects are still insufficient, and more improvement is required. For example, state of the coated surface is still poor, and stability with time against scratch is insufficient.